1. Field of the Invention
This invention relates to vessel propulsion systems, and in particular to a self-contained hydraulic thruster for vessel.
2. Background of the Invention
Marine thrusters typically mount on barges and flat boats, and are used as propulsion for these vessels. One type of marine thruster employs a prime mover such as a diesel engine driving a hydraulic pump, together known as a “power pack”, and the resultant pressurized hydraulic fluid may be employed to drive a propeller attached to a lower unit.
There are a number of problems associated with currently available marine thrusters. Where a centrally located tiltable lower unit has been retracted and tilted backwards for transportation, storage, maintenance, cleaning, etc., the protruding upper end of the lower unit interferes with the helm and helm platform, and prevents full upward tilting of the retracted lower unit. Therefore, it would be desirable to provide a marine thruster which may be retracted and then fully tilted.
Another problem with existing designs: the hydraulic fluid reservoir is disposed on the base of the marine thruster, where it is incapable of supplying enough fluid head to self-prime the power pack, and to facilitate hydraulic fluid flow to the hydraulic power pack. Thus, it would be desirable to provide a hydraulic fluid reservoir which is elevated to a substantial height above the level of the base upon which the power pack is mounted.
Still another problem is where a marine thruster's single lower unit propeller does not supply enough power to adequately propel a vessel upon which it is mounted. It would therefore be desirable to provide a marine thruster with more than one lower unit, for increased power.
Existing Designs
FIGS. 1 and 2 are illustrative of the tilt interference problem, and are rear views of a prior art marine thruster 2. The location of their lower units 4 directly behind their respective helms 6 causes interference between lower unit 4 and helm 6 when attempting to fully tilt lower unit 4 up when lower unit 4 is fully retracted. This interference prevents lower unit 4 from fully tilting up when it is fully retracted, thus hindering stowing of lower unit 4 for storage, transportation, servicing, cleaning, etc.
In addition, the mounting of the hydraulic fluid reservoir on the base of this design provides inadequate flow from the hydraulic fluid tank for self-priming and gravitational flow from the hydraulic fluid tank to the power pack.